This invention relates to an apparatus for detecting the emission of radiation from a sample having a low level of radioactivity and more particularly to an apparatus which is inexpensive and efficient.
Waste having low levels of radiation is created at nuclear power plants and the like. Typically, the waste comprises paper, fabrics, boots, clothing, tools and various other items which can normally be expected to be used in the laboratories, offices, workshops and the like of a nuclear facility. Prior to its disposal the waste is collected in containers and is taken through a series of inspections during which it is inspected for beta particle and gamma ray emissions.
To the extent that radioactive emissions above predetermined levels are detected, the waste-filled containers are disposed of as hazardous by being buried at controlled disposal sites. The contents of the container are not subjected to further inspection due to the low likelihood of finding uncontaminated articles. Usually radiation in excess of two milliroentgens per hour from the container is considered to be the point above which there is a low likelihood of finding salvagable material.
Waste which exhibits radiation which is less than two milliroentgens per hour is subjected to closer inspection in an attempt to remove its nonradioactive components. This reduces the volume of material that must be buried at controlled sites and provides an opportunity to recover valuable items such as tools.
An aspect of inspecting waste relates to an inspection for low level gamma ray emission. To accomplish this inspection, waste which is generally considered to be relatively free from gamma radiation is placed in plastic bags or cardboard boxes. The waste may be compacted if desired prior to its inspection to increase the quantity of material being examined.
A process for the preliminary examination of the waste of which the apparatus disclosed herein can be a part is disclosed in co-pending patent application Ser. No. 648,780 enittled METHOD FOR SORTING RADIOACTIVE WASTE which was filed by Alfred N. Johnson and Anthony J. Prisco on Sept. 10, 1984.
The method apparatus disclosed herein is operative to detect the gamma radiation emanating from a sample while minimizing interference from background radiation. This is accomplished by locating shielding around the gamma ray detector and around the apparatus